A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope (lens capsule), varying in degree from slight to complete opacity and obstructing the passage of light. Early in the development of age-related cataract, the power of the lens may be increased, causing near-sightedness (myopia), and the gradual yellowing and opacification of the lens may reduce the perception of blue colors. Cataracts typically progress slowly to cause vision loss, and are potentially blinding if untreated. The condition usually affects both eyes, but almost always one eye is affected earlier than the other. The following is a list of different types of cataracts:
Senile cataract—Characterized by an initial opacity in the lens, subsequent swelling of the lens, and final shrinkage with complete loss of transparency occurring in the elderly.
Morgagnian cataract—Liquefied cataract cortex forming a milky white fluid, which can cause severe inflammation if the lens capsule ruptures and leaks, occurring as a progression of the cataract. Untreated, the advanced cataract can cause phacomorphic glaucoma. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly.
Cataract resulting from trauma—A cataract resulting from trauma to the eye in an otherwise healthy individual. Blunt trauma or penetrating trauma resulting from accidental injury to the eye can result in crystalline lens opacification. Retinal surgery involving a para plana vitrectomy will result in a post-operative cataract in six to nine months after the surgery. Infrequently, an adverse event can occur where by the otherwise healthy crystalline lens is touched by a surgical instrument during retinal surgery. The crystalline lens clouds and a cataract forms within minutes of the contact.
Congenital cataract—A cataract developed in a child before or just after birth.
In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 and 64, 60% of those between the ages 65 and 74, and 91% of those between the ages of 75 and 85.
Age-related cataract is responsible for 48% of world blindness, which represents about 18 million people, according to the World Health Organization. Continued population growth with the shift of the average age will result in increased numbers of patients with cataracts. The increase in ultraviolet radiation resulting from depletion of the ozone layer is expected to further increase the incidence of cataracts.
In many countries, surgical services are inadequate, and cataracts remain the leading cause of blindness. Cataracts are a large cause of low vision in both developed and developing countries. Even where surgical services are available, low vision associated with cataracts can remain prevalent, as a result of long waits for operations and barriers to surgical uptake, such as cost, lack of information and patient transportation problems.
Several factors can promote the formation of cataracts, including long-term exposure to ultraviolet light, exposure to ionizing radiation, secondary effects of diseases such as diabetes, hypertension and advanced age, or trauma (possibly much earlier); they are usually a result of denaturation of lens protein. Genetic factors are often a cause of congenital cataracts, and positive family history may also play a role in predisposing someone to cataracts at an earlier age, a phenomenon of “anticipation” in presenile cataracts. Cataracts may also be produced by eye injury or physical trauma.
A study among Icelandair pilots showed commercial airline pilots are three times more likely to develop cataracts than people with nonflying jobs. This is thought to be caused by excessive exposure at high altitudes to radiation coming from outer space, which becomes attenuated by atmospheric absorption at ground level. Supporting this theory is the report that 33 of the 36 Apollo astronauts involved in the nine Apollo missions to leave Earth orbit have developed early stage cataracts that have been shown to be caused by exposure to cosmic rays during their trips. At least 39 former astronauts have developed cataracts, of whom 36 were involved in high-radiation missions such as the Apollo missions.
Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers, who suffer from exfoliation syndrome. Exposure to microwave radiation can cause cataracts. Atopic or allergic conditions are also known to quicken the progression of cataracts, especially in children. Cataracts can also be caused by iodine deficiency. Cataracts may be partial or complete, stationary or progressive, or hard or soft. Some drugs can induce cataract development, such as corticosteroids and the antipsychotic drug quetiapine (sold as Seroquel, Ketipinor, or Quepin).
The operation to remove cataracts can be performed at any stage of their development. There is no longer a reason to wait until a cataract is “ripe” before removing it. However, since all surgery involve some level of risk, it is usually worth waiting until there is some change in vision before removing the cataract.
The most effective and common treatment is to make an incision (capsulotomy) into the capsule of the cloudy lens to surgically remove it. Two types of eye surgery can be used to remove cataracts: extra-capsular cataract extraction (ECCE) and intra-capsular cataract extraction (ICCE). ECCE surgery involves removing the lens, but leaving the majority of the lens capsule intact. High frequency sound waves (phacoemulsification) are sometimes used to break up the lens before extraction. ICCE surgery involves removing the lens and lens capsule, but it is rarely performed in modern practice. In either extra-capsular surgery or intra-capsular surgery, the cataractous lens is removed and replaced with an intraocular plastic lens (an intraocular lens implant) which stays in the eye permanently. The intraocular lens is placed into a cartridge and inserted through the small surgical incision. The inserter folds the intraocular lens and pushed it through a small needle. The end of the needle is positioned within the capsular bag. When the folded intraocular lens exits the end of the needle, it slowly unfolds as the surgeon manipulated the lens into its final position. Cataract operations are usually performed using a local anesthetic, and the patient is allowed to go home the same day. Until the early twenty-first century intraocular lenses were always monofocal; since then improvements in intraocular technology allow implanting a multifocal lens to create a visual environment in which patients are less dependent on glasses. Such multifocal lenses are mechanically flexible and can be controlled using the eye muscles used to control the natural lens.
Complications are possible after cataract surgery, including endophthalmitis, posterior capsular opacification, and retinal detachment.
Laser surgery involves cutting away a small circle-shaped area of the lens capsule, enough to allow light to pass directly through the eye to the retina. There are, as always, some risks, but serious side effects are very rare. As of 2012, research into the use of extremely-short-pulse (femtosecond) lasers for cataract surgery was being carried out. High frequency ultrasound is currently the most common means to extract the cataract lens.
Cataract surgeries are conducted in an operating room under sterile conditions to prevent the risk of infection, particularly endophthalmitis; a rapid devastating infection that can cause blindness in a few days. The patient's eye is cleaned with an antiseptic, and then isolated with a sterile drape that fully covers the patient with only the eye exposed. A sterile field is established around the patient such that any personnel or instrumentation must be suitably scrubbed, draped or sterilized following standard aseptic procedures.
With reference to FIGS. 1 and 2, such a prior art type of cataract surgery includes using a surgical microscope to view the interior of the eye through a patient's cornea and iris. The surgeon typically makes two incisions 10, 12 in the patient's cornea, close to the limbus, to enable surgical instruments to gain access to the interior segment of the eye and to implant an intraocular lens after the cataract crystalline lens has been removed. For example, an intraocular lens inserter 14 can be inserted through the incision 10 and a positioning device 16 can be inserted through the incision 12.
The surgery typically includes creating a full-circle tear in the center of the capsular bag on the interior side, called a “capsulorhexis,” and removing the torn circle of the capsule. Then, the cataract crystalline lens is removed using a phacoemulsifier, an ultrasonic infusing and aspirating instrument that breaks up the cataract and aspirates the fragments, removing the cataract.
The lingering cortical material that is attached to the inner surface of the capsular bag is then aspirated using an infusion/aspirating instrument. The intraocular lens 18 is then inserted using the lens inserter 14 and positioned within the capsular bag using the positioning device 16 or other devices.
The lens inserter 14 transfers the flat intraocular lens 18 through the small clear corneal incision 10 into the capsular opening (capsulorhexis) and to its final position within the capsular bag. The inserter 14 pushes the flat lens 18 through a cartridge which causes the lens to fold and pass through a tubular portion of the cartridge which is placed into the small incision 10. As the lens 18 emerges out of the tubular end of the cartridge 14, it slowly unfolds and returns to its original flat shape.
Recent advances in femtosecond laser instrumentation has automated the process of making entry incisions and the capsulorhexis as well as pre-cutting the cataract making the cataract surgical procedure more precise, safer, and easier for the surgeon to execute.
The majority of current lens inserters are manually operated re-usable instruments with primarily one of two methods to push the lens: a lead screw or plunger. The lead screw approach provides consistent and smooth delivery of the lens, however slowly, and requires the surgeon or an assistant to turn the manual lead screw as the surgeon positions the tip of the instrument.
The plunger approach does not require an assistant, as the surgeon uses their thumb to drive the lens forward, much like injecting a drug from a syringe. Additionally, the surgeon can more readily control the speed of delivery, swiftly moving though the less critical portions and slowing for the more delicate segments. A draw back of the plunger approach can emerge when the lens becomes stuck resulting in a more forceful push by the surgeon where upon clearance of the hang-up, the lens can over-shoot its exit and injure the patient.
Recently, efforts have been made to perform such lens replacement surgeries using smaller corneal incisions. For example, as shown schematically in the illustration of FIG. 3, typically, the distal end of an intraocular lens inserter 14 is inserted completely through the incision 10, during a procedure of inserting an intraocular lens 18.
However, with reference to FIG. 4, recently surgeons have been adopting a “wound-assist” technique, wherein only a small portion of the tip 20 of the intraocular lens inserter 14 is inserted into the incision 10, wherein the incision 10 is smaller than the incisions previously made, such as during the procedure illustrated in FIG. 3. As such, the intraocular lens 18, in its folded state, is pushed through and slides along interior surfaces of the incision 10. This allows the incision 10 to be smaller and the wound itself (incision 10) becomes a lumen for inserting the lens 18 into the eye.
During such a procedure, the surgeon can use the distal end 20 of the tip of the intraocular inserter 14 to help hold the incision 10 open. For example, the surgeon might apply a lateral force in the direction of arrow 22 in order to hold the incision 10 open such that the lens 18 can be pushed therethrough.